Bio-augmentation with dissimilatory nitrate reduction to ammonium (DNRA) driven sulfide-oxidizing bacteria enhances the durability of nitrate-mediated souring control.

Biological souring (producing sulfide) is a global challenge facing anaerobic water bodies, especially the oil reservoir fluids. Nitrate injection has demonstrated great potential in souring control, and dissimilatory nitrate reduction to ammonium (DNRA) bacteria was proposed to play crucial roles in the process. How to durably control souring with nitrate amendment, however, remains undiscovered. Herein, Gordonia sp. TD-4, a DNRA-driven sulfide-oxidizing bacterium, was used to elucidate the effects of bio-augmentation with DNRA bacteria on the durability of nitrate-mediated souring control. The results revealed that nitrate amendment combined with bio-augmentation with TD-4 after souring could effectively control souring and enhance the durability of nitrate-mediated souring control, while nitrate amendment before souring failed to persistently control souring. Nitrate amendment before and after souring resulted in different evolution dynamics of nitrate-reducing bacteria. Denitrifying bacteria were enriched in reactors amended with nitrate before souring or in dissolved sulfide exhausted reactors amended with nitrate after souring. The heterotrophic denitrifying activity of denitrifying bacteria, however, decreased the durability of nitrate-mediated souring control. Comparative and functional genomics analysis identified potential niche adaptation mechanisms (autotrophic and heterotrophic nitrate/nitrite reduction, including DNRA and denitrification) of predominant SRB in nitrate-amended environments, which were responsible for the rapid resumption of sulfide accumulation after the depletion of nitrate and nitrite. Pulsed injection of nitrate combined with bio-augmentation with DNRA-driven sulfide-oxidizing bacteria was proposed as a potential method to enhance the durability of nitrate-mediated souring control. The findings were innovatively applied to simultaneous bio-demulsification and souring control of emulsified and sour produced water from the petroleum industry.

Stress proteins, nonribosomal peptide synthetases, and polyketide synthases regulate carbon sources-mediated bio-demulsifying mechanisms of nitrate-reducing bacterium Gordonia sp. TD-4.

Carbon sources have been reported to determine the bio-demulsifying performance and mechanisms. However, the genetic regulation of carbon sources-mediated bio-demulsification remains unclear. Here, the effects of ß-oxidation, stress response, and nitrate metabolism on the demulsification of alkaline-surfactant-polymer flooding produced water by Gordonia sp. TD-4 were investigated. The results showed that competitive adsorption-derived demulsification was mediated by oil-soluble carbon sources (paraffin). Surface-active lipopeptides responsible for competitive adsorption-derived demulsification could be biosynthesized by the nonribosomal peptide synthetases and polyketide synthases using oil-soluble carbon sources. Bio-flocculation-derived demulsification was mediated by water-soluble carbon sources. Water-soluble carbon sources (sodium acetate and glucose) mediated the process of the dissimilatory reduction of nitrate to ammonia, which resulted in the variable accumulation of nitrite. The accumulated nitrite (>180 mg-N/L) stimulated stress response and induced the upregulation of chaperone-associated genes. The upregulation of chaperonins increased the cell surface hydrophobicity and the cation-dependent bio-flocculating performance, which were responsible for bio-flocculation-derived demulsification. The ß-oxidation of fatty acids significantly affected both competitive adsorption-derived demulsification and bio-flocculation-derived demulsification. This study illustrates the synergistic effects of nitrogen sources and carbon sources on the regulation of bio-demulsifying mechanisms of TD-4 and identifies two key functional gene modules responsible for the regulation of bio-demulsifying mechanisms.

Is anammox a promising treatment process for nitrogen removal from nitrogen-rich saline wastewater?

Rapidly growing discharge of nitrogen-rich saline wastewater has significantly affect environment. However, due to the inhibition resulting from high salinity on microbes, it is still a challenge to treat nitrogen-rich saline wastewater efficiently. Anammox process, as a cost-effective and environment-friendly nitrogen removal approach, has shown a potential in treating nitrogen-rich saline wastewater. This review is conducted from a critical perspective and provides a comprehensive overview on the performance of anammox process treating nitrogen-rich saline wastewater. Two strategies including freshwater-derived anammox bacteria acclimatization and marine anammox bacteria enrichment are evaluated. Second, effects resulting from salinity on the performance of anammox reactor, the microbial communities and sludge characteristics are discussed. Third, salinity-tolerant mechanism of anammox bacteria is analyzed. This review also reveals some critical knowledge gaps and future research needs, which benefits application of anammox process to treat nitrogen-rich saline wastewater.

[Nitrogen Removal Performance of ANAMMOX with Different Organic Carbon Sources].

Anaerobic ammonium oxidation (ANAMMOX) has been regarded as an efficient process to treat high-strength wastewater without organic carbon source. To investigate the nitrogen removal performance of ANAMMOX in the presence of organic carbon source can broaden its application in organic wastewater treatment. In this work, an anaerobic sequencing batch reactor (ASBR) was used to study the effect of organic carbon source on ANAMMOX process. The experimental results indicated that the activity of anaerobic ammonia oxidizing bacteria (AAOB) decreased by 84.2% when 200 mg·L-1 COD of glucose was added. When sodium acetate was added, the activity of AAOB was affected little. Besides, it even promoted the activity with COD less than 120 mg·L-1. The effect of sucrose on ANAMMOX process was similar to that of sodium acetate and the maximum specific ANAMMOX activity (SAA) increased by 25.0% with 80 mg·L-1 COD. When citric acid was added, the maximum SAA peaked with 80 mg·L-1 COD. The order of ANAMMOX promotion resulted from organic carbon source was sucrose, sodium acetate, citric acid and glucose. With addition of organic carbon source, nitrate could also be removed through the synergy of ANAMMOX and denitrification, and the total nitrogen removal efficiency increased.

[Recovery Performance of ANAMMOX Process after Inhibition Resulting from Seawater].

An anaerobic sequencing batch reactor (ASBR) was operated to investigate the recovery performance of ANAMMOX reactor after the inhibition of 100% seawater concentration. The results showed that the nitrogen removal performance of ANAMMOX reactor suffered inhibition of high salinity concentration. However, it could enter a period of stable nitrogen removal efficiency again after an interim stable period and a recovery period. The nitrogen removal rate (NRR) could reach 0.52 kg·(m3·d)-1, which was similar to the control group, containing 10% seawater and having a NRR of 0.462 kg·(m3·d)-1. The modified Logistic model and modified Gompertz model were revised and their application field was broadened. The re-modified Logistic model was suggested to be used to simulate the NRR recovery process of ANAMMOX reactor that suffered inhibition of 100% seawater concentration. The doubling time of NRR was calculated to be 11.359 d using the prediction formula established for the recovery time of NRR.